Most commercially available MEMS acoustic sensors or microphones are formed by two chips, an application specific integrated circuit (ASIC) chip and a MEMS chip attached to a substrate. These chips are conventionally enclosed by a conductive cover or lid. An acoustic input can be provided from an opening on a top surface of the acoustic sensor or from an opening on the substrate. Typically, in commercial applications where the acoustic input is from the top, an acoustic back cavity is formed mainly by a volume under the MEMS chip and the substrate. By contrast, in commercial applications where the acoustic input is from the bottom, the acoustic cavity is typically formed by the volume enclosed by the substrate and the cover.
The performance of a conventional acoustic sensor is dependent on having an adequate area for both acoustic sensing and electrical transduction; however the cost and functionality of the microphone puts a limit on the package size. These two sets of opposing and competing requirements often require some form of compromise.
It is desirable to provide improvements to MEMS acoustic sensors which allow the sensors to be more easily manufactured at a lower cost and have improved performance. The improved MEMS acoustic sensor must be easily implemented, cost effective and adaptable to existing manufacturing processes.
The present invention addresses such a need.